A thermal shutdown (TSD) circuit is a type of circuit that is often found in linear and switching regulators and power management devices. Almost all power regulator and converter integrated circuits have an on-chip thermal shutdown circuit that monitors the temperature of the integrated circuit die.
Prior art thermal shutdown circuits are usually designed to continually sense the temperature of an integrated circuit die (referred to as “the die temperature”). When the die temperature increases to a preselected threshold value of temperature (referred to as “the shutdown temperature”), the thermal shutdown circuit abruptly cuts off power to the integrated circuit. This results in an immediate shut down of the operations of the integrated circuit. A typical preselected shutdown temperature is about one hundred forty degrees Celsius (140° C.). Shutting down the operation of an integrated circuit at a shutdown temperature of 140° C. prevents further system damage due to heat and prevents fire hazards. Depending upon the circuit application involved, the preselected shutdown temperature may be in a range from about one hundred thirty degrees Celsius (130° C.) to one hundred seventy degrees Celsius (170° C.).
The abrupt cut off of power to a system is unacceptable for many of the complex and sophisticated portable devices in general use today (such as cellular phones, personal digital assistants, audio-video recording systems, etc.). Abruptly shutting down an electronic system (or any of its subsystems) without warning due to internal overheating or high ambient temperature can cause problems. The problems may range from simple inconvenience to the loss of data or even to damage to the system. Therefore the abrupt cut off of power to a system is to be avoided.
Some more sophisticated prior art approaches to the problem have utilized a dedicated temperature sensor integrated circuit that monitors the local temperature level. The temperature integrated circuit communicates temperature information to a host controller unit via a communications bus. The temperature integrated circuit is able to provide the host controller unit with warning signals that indicate the occurrence of increased levels of temperature. The warning signals give the host controller unit sufficient time to respond and initiate a timely shutdown sequence of operations before a critical temperature level is reached. The dedicated temperature sensor integrated circuit approach requires additional cost, additional area, and additional overhead to perform the temperature sensing function.
A dedicated temperature integrated circuit may be useful to manage global heating due to external ambient temperature for a portable electronic system. However, a dedicated temperature integrated circuit may not be useful to manage a localized increase in temperature (e.g., caused by an unscheduled high power dissipation or by a malfunction in some internal circuitry). For example, consider a cellular phone that has a power management unit integrated circuit (PMUIC). The PMUIC may contain a dozen or so voltage regulators. In addition, there may also be several more stand alone regulators distributed around the system board to power the power amplifier (PA), radio frequency (RF) low power amplifiers (LPA), temperature compensated crystal oscillator (TCXO), multimedia audio system, and other similar elements. A centralized thermal management system is not adequate to manage localized increases in temperature in such an extended system.
It would be advantageous to have a thermal shutdown (TSD) circuit that would not abruptly cut off power to a system that experiences a localized increase in temperature.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; “each” means every one of at least a subset of the identified items; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior uses, as well as future uses, of such defined words and phrases.